My invention relates to a shoring device comprising a piston, cylinder, and an outer cam collar combined with an inner ring. More particularly, this invention relates to a shoring device for trenches with a removable rotating outer cam collar. This outer cam collar encloses an inner ring with a continuous circular indentation along the inner ring circumference. This inner ring also comprises an inner continuous circular lip. My new outer cam collar insures that the partially enclosed piston does not rotate during use. My new shoring device is intended for, but not exclusively, public works and construction, rescue and other projects in which shoring is necessary.
As workers shore trenches, they must quickly install shoring to prevent collapse of the trench walls. If shoring is not installed, soil cohesion is lost and it becomes almost impossible to maintain a safe trench. The prior art as best depicted in expired U.S. Pat. No. 3,851,856(Berg) provides a shoring device with an inlet connecting to a pressure source for expanding the device tightly against trench walls. There is also a cylindrical collar mounted on one cylinder end, which receives the piston. This cylindrical collar extends axially from the cylinder and surrounds the proximal piston end.
Still referring to the Berg device, the cylindrical collar comprises two camming surfaces along the cylindrical collar's proximal edge. Subsequent to cylinder pressurization the piston remains extended by the securing of one camming surface with a pin. In addition, a threaded stud abuts and tightens against the cylinder by an attached handle. This threaded stud penetrates the rotating collar and abuts the cylinder after the cam pin is placed against the camming surface.
This abutting threaded stud prevents relative rotation of the cylindrical collar to the cylinder. The threaded stud also locks the cylindrical collar against the pin, thereby preventing the rotating collar from loosening. However, this threaded stud is the only structure in Berg's device which prevents the cylindrical collar from rotating after cessation of the gas pressure.
Furthermore, Berg's threaded stud only contacts one point along the cylinder exterior surface and weakens the cylinder structure after each application. Inevitably, the entire cylinder must be replaced, and this replacement is expensive and time consuming. In contrast, my continuous circular indentation prevents the flat threaded pin furthermost point from skidding along the cylinder surface. The cylinder is not weakened by repeated contract, because the outer cam collar provides the direct contact surface. My outer cam collar is more economical to replace, and protects the cylinder from wear and tear from the threaded pin.
In addition, my inner ring comprises a continuous circular lip which abuts the piston and prevents it from falling from the cylinder or becoming a projectile during operation.
My new inner ring engages one cylinder end, thereby reducing the possibility that the piston will fall from the cylinder during operation. This metal lip abuts the piston to prevent piston lateral movement, which is an important safety advantage which the Berg device does not have.
In my invention the outer cam collar encloses the inner ring and comprises the threaded pin which tightly abuts the circular continuous indentation. The cam edges, together with a straight metal cam pin, prevent counter-clockwise rotation of the outer cam collar. My improved shoring device is engineered to assist underground workers in compliance with the OSHA regulation governing excavations, i.e., 29 C.F.R. 1926.650. This group includes, but is not limited to, sewer contractors, plumbers, gas companies, telephone companies, municipal public works departments and fire rescue services. The principle goal of my shoring device is to provide the necessary physical support which ensures a work environment safe from collapse.
In particular, shoring is the placement of cross bracing and other components within a trench to support trench walls. There are two important theories of shoring: first is the theory of “zero-movement”, in which shoring is designed to prevent wall movement. Shoring is not sufficiently strong to retain a moving wall of soil: it merely prevents a soil wall from initially moving. The second theory of shoring is designated the “Arch Effect.” Shoring is effective because it creates forces as it pushes again trench walls. The network of cross braces and uprights or wale-plates creates an arch effect which retains soil. The shoring and cross bracing actually retains soil, and not the plywood or sheeting.
An operator applies plywood or sheeting to prevent surface soil from falling and injuring a worker. To achieve “zero movement” and the “arch effect,” all gaps and voids must be filled where the cross brace bears on the trench wall. Other than the mandatory inspection for damage before each use and an occasional cleaning, there are no maintenance requirements.
My preferred pneumatic shoring device also comprises a contiguous pressurized gas channel through the cylinder to the piston. In the best mode, this contiguous pressurized gas channel includes a circular channel segment along the lower floor surface of a cylinder rubber end cup.